As is widely known source IP Address spoofing is a common technique used in denial of service attacks (DoS). Other types of source IP address spoofing attacks are widely known, and include attacks such as distributed denial of service attacks (DDoS), Worm attacks, and Man In the Middle attacks. Spoofed Source IP Address attacks can also include Smurf attacks, NameServer attacks, and ICMP, IGMP, and UDP protocol attacks. One goal in some spoofing attacks is to spread a software virus to as many random new victims as possible, and other attacks are designed to overwhelm a computer system, and other attacks are used to steal information.
FIG. 1 shows a computer network 100 of the prior art. At the lowest layer (layer 1 of the OSI Networking protocols) is the physical layer which describes the actual physical elements such as cables and connectors which connect different devices of the computer network. The next layer of the system is the layer 2, the datalink layer. At this level, among other things, the MAC addresses are used to identify the devices which are interconnected on a subnet. As is widely known a MAC address is a unique address which corresponds to a device connected to a network. The MAC address is generally determined by the Ethernet board of a device which is connected to the network.
The computer network 100 can have a number of subnets. As shown in FIG. 1, the subnets are 102, 104, 106, and 108. Each subnet can contain a number of layer 2 devices such as switches. For example, subnet 102 is shown as having switches 110-126, and subnet 104 is shown as having switches 128-134. The layer 2 devices are not shown for subnets 106 and 108, but as one of skill in the art will appreciate, most subnets will include a number of layer 2 devices such as switches or hubs. Each switch can have a number of ports to which additional switches can be coupled, or to which host devices such as end user computers, or serves, or mainframes can be connected. At the subnet level different devices are connected to the subnet and can communicate with other devices on the subnet by transmitting data packets through the switches. These data packets include the MAC address for the device to which the data packet is to be sent (the destination MAC address) and the MAC address for the host which is sending the packet (the source MAC address). In addition each host device will be assigned an IP address. The IP address is utilized by a router 136 to determine routing for data packets which are being sent by a host on one subnet to a host on a different subnet, or to a different device which may require that the packet be transmitted via the Internet 138. The IP address is often assigned using the Dynamic Host Configuration Protocol (DHCP). Each host on a subnet will normally be assigned an IP address. As is widely known data packets generated by a host on the subnet can include information which is being sent from one host to another host, and further these data packets will include MAC addresses as described above, and a source IP address and a destination IP address.
Source IP spoofing occurs when an attacker host uses a source IP address, which does not correspond, or is not assigned, to its MAC address, in a transmitted data packet. For example, the attacker host may select a source IP address for a different host on a different subnet and transmit a data packet with this false, or spoofed, IP address. This data packet would then be received by the destination device, and the destination device would read the spoofed IP address and it would appear to the destination device that the data packet had come from the device which is actually assigned the source IP address which was used by the attacker host.
In terms of network security defenses, traditional blocks to this type for source IP spoofing were to create inbound filters on the router ports 140-146 that supported the subnets 102-108. The router filter operates such that it knows which IP addresses should be received from a specific subnet connected to the particular port. This allows ISP's and enterprises to block randomly spoofed source IP addresses, where the spoofed IP address received on a particular port of the router, is not consistent with source IP addresses for the subnet which is coupled to the particular port of the router. Hackers have recognized the limitations inherent in this type of source IP address anti-spoofing process, and developed spoofing software tools, some of which are referred to as “zombies, and “bots” which now spoof source IP addresses from within their own subnet and subnet mask settings. For customers with large class B subnets, the router level (layer 3) type of defense is not very effective as hundreds and potentially thousands of hosts on the subnet can still be affected.
An Automatic Spoof detector (referred to as “Spoofwatch”) has been developed in an attempt to efficiently detect hosts performing source IP spoofing. Spoofwatch works on the premise that these hosts do not respond to ARP requests for their spoofed IP addresses. This solution has many potential shortcomings. For example, the router 136 can receive very large numbers of different source IP addresses in different data packets. Thus, a very large amount of router's processing power is consumed with generating the ARP requests and monitoring the responses.
A review of a number of different websites related to networking showed a number of different approaches related to preventing IP address spoofing, but each approach was very different than that discussed herein. Other techniques have been developed for providing defenses against source IP address spoofing. One of these other approaches relies on using encryption, and source IP filtering at the layer 3 level, which is after the data packets have been transmitted from the subnet to the router.
Additional information regarding different approaches to combating source IP spoofing can be found at http://www.cisco.com/en/US/tech/tk86/tk803/technologies_tech_note09186a00800a7828.shtml. Additional websites provide discussion regarding the risks associated with source IP address spoofing and provide some discussion for ways to combat spoofing, see for example: http://www.sans.org/rr/threats/spoofed.php; http://www.cert.org/incident_notes/IN-2000-04.html; http://www.anml.iu.edu/PDF/Automatic_Spoof_Detector.pdf; and http://www.linuxgazette.com/issue63/sharma.html.
In order to increase the efficiency and effectiveness of combating source IP spoofing it would be beneficial to provide source IP spoofing at lower level in the network hierarchy, in a manner which has not previously been provided.